So have had 6 Discos over the past 10 years and am very familiar with the 4.0 and getting to be familiar with the 4.6.
Long story short I am at my wits end chasing an issue on an 03 Disco II.
It is backfiring through all intake parts (upper plenum removed and end started to verify this - Flames shot out of each individual port). Fuel Pressure is in the 60-65 PSI range when it should be around 37psi. The funny thing is it only backfires and hesitates under heavy quick throttle. If the throttle is eased up to 3000rpm all is fine. I'm pretty sure timing is OK because it idles with no issues and only has random misfires under heavy load or mash on throttle.

Anyone out there with ideas?? I'm loosing my mind on this one.

 

For this to happen, all intake valves are open when the engine is firing. How many miles is on the engine? Sounds kind of like the cam chain could be very worn and sloppy, or could be the crank sensor or the camshaft sensor. There is something called valve overlap, whereas at the end of the exhaust stroke, the intake valve is opening while the exhaust valve is closing,(around top dead center) to help evacuate the exhaust from the combustion chamber while the fuel/air mixture starts enter the chamber. Is your CEL on, and what codes if any are showing up?

 

Joemamma1954 Thank you for the reply... There is 103K on the engine.
The codes are P308 misfire) P1884 (TCM Error) P0102 (MAF error) P1412 (Secondary air error) P1590 (P1590 not related - ABS)

 

I also believe your fuel pressure is right where it should be. 37lbs would be too low.
Also there are many posts on the P1884 and if i recall it has to do with the MAF also.

 

you have an ignition problem on your High tension side, check your ht wires , replace them, and also your coils that seats behind de intake manifold close to firewall

 

I seriously doubt that it is the coil or wires. The crankshaft sensor, is the most important sensor and it lets the ecm know the crankshaft and pistons position and the ecm sends the spark signal to the coils.(at the appropriate time). For all of them to be firing early or late, it could be the CKS itself or the flywheel (tabs where the CKS picks up its signal from).
For all the cylinders to be backfiring thru the intake, either the timing of the spark is off, or the valve timing is off.

 

sorry to degagree with you everything you are saying is fine an dandy but the only thing NON ELECTRONIC is the compression if is 30 psi all across defenetly
is timing chain . out of timing MECHANICALLY

 

Please accept my appologies I wrongly sen you a reply, that one was for the member
cabrera
with de low compression in a disco ll
regards
jaime

 

The 37psi number quoted was referring to fuel pressure, not cylinder pressure.

However, just coils or wires are unlikely to cause backfires unless things are firing so inefficiently that there's a buildup of fuel that then ignites as a backfire -- but then the OP should be seeing many more misfire codes. This does sound like a timing issue to me, but it's hard to say whether it's ignition (in which case crank position sensor) or valve (timing chain).

 

No apolgies necessaryl, I wasnt trying to call you out or anything. Just looking at things from my experience and point of view. Any help and comments are viewed and appreciated. Rock on Brother.